Nanoparticles (NPs) defined as particles having at least one dimension below 100 nm have been applied in the last decade in industry and medicine. Recently, there is an increased concern about the biohazard aspect of the presence of NP in consumer goods and in the environment. Silver NP (Ag NP) cause oxidative stress in mammalian cells in result of generation of reactive oxygen species (ROS). This results in genotoxicity and mutagenicity, disturbed mitochondrial respiration, slowed proliferation and cell death. Using the alkaline comet assay, we examined the effect of combined treatment with Ag NP 20 nm or 200 nm and X-rays (2 Gy) in HepG2 cells. In addition, combined treatment with X-rays and titanium dioxide NP (TiO2 NP) 21 nm was also studied. No effect of NP pre-treatment on X-ray induced initial deoxyribonucleic acid (DNA) damage levels was observed for all three NP. In contrast, Ag NP treatment preceding exposure to X-rays caused a marked decrease in the rate of single strand break rejoining. The effect was particularly strong for Ag NP 20 nm. TiO2 NP pre-treatment had no effect on DNA repair.
We compared three methods usually applied in biological dosimetry for estimation of radiation-induced DNA damage in human T and B lymphocytes: alkaline comet assay, micronucleus (MN) test and formation of histone gamma-H2AX foci. Human peripheral blood lymphocytes were fractionated using T cells and B cells isolation kits. Cells were irradiated with doses in the range of 0-1 Gy of X-rays. Induction of DNA damage was assessed by the standard alkaline comet assay, MN test and histone gammaH2AX foci immunofluorescence assay. Notwithstanding different end-points measured by the applied methods, all tests revealed a similar induction of DNA damage in B lymphocytes as compared with T lymphocytes. The results indicated that all three tests detect DNA damage with similar sensitivity, the lowest dose being approximately 0.3 Gy. The difference between irradiated and control cells was expressed as the ratio of the value obtained for irradiated cells (1 Gy) to that for control cells. The highest ratio was obtained for formation of gammaH2AX foci and was 6.2 for T and 13.8 for B lymphocytes, whereas those for comet assay and micronucleus test were 3.5; 3.6 and 5.6; 4.8, respectively.
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